Examples of a method of realizing a high density of an optical disc include a method of realizing a high density in a linear density direction by shortening a channel bit length, that is, a mark length, and a method of narrowing a track pitch. However, when realizing the high density in the linear density direction, a problem related to an increase in inter-code interference occurs. In addition, when the track pitch is narrowed, leakage (adjacent track crosstalk) of information from an adjacent track increases. A method of reducing the adjacent track crosstalk (hereinafter, simply referred to as “crosstalk”) is suggested.
For example, Patent Document 1 discloses a configuration in which respective reproduction signals of a current reproduction track and tracks on both sides thereof are supplied to an adaptive equalizer unit, and a tap coefficient of the adaptive equalizer unit is controlled to remove the crosstalk.
In addition, Patent Document 2 and Patent Document 3 disclose the following configuration. Reflected light from an optical recording medium is spatially divided into three light beams in a track width direction, and the three light beams which are divided are respectively detected. Detection signals are multiplied (weighed) with a constant and are subjected to addition computation to reduce an effect of the crosstalk. In addition, Patent Document 2 implies a configuration in which weighing is performed even in a beam propagation direction so as to reproduce a reproduction signal of a small recording mark in an emphasizing manner as an idea.